Kinetic study of single-walled carbon nanotube synthesis by thermocatalytic decomposition of methane using floating catalyst chemical vapour deposition

Synthesis of MWCNTs by chemical vapor deposition of methane using FeMo/MgO catalyst: role of hydrogen and kinetic study

This study aims to investigate the role of hydrogen on CNTs synthesis and kinetics of CNTs formation. The CNTs were synthesized by catalytic chemical vapor deposition of methane over FeMo/MgO catalyst. The experimental results revealed that hydrogen plays an important role in the structural changes of catalyst during the pre-reduction process. The catalyst structure fully transformed into metallic FeMo phases, resulting in an increased yield of 5 folds higher than those of the non-reduced catalyst. However, the slightly larger diameter and lower crystallinity ratio of CNTs was obtained. The hydrogen co-feeding during the synthesis can slightly increase the CNTs yield. After achieving the optimum amount of hydrogen addition, further increase in hydrogen would inhibit the methane decomposition, resulting in lower product yield. The hydrogenation of carbon to methane was proceeded in hydrogen co-feed process. However, the hydrogenation was non-selective to allotropes of carbon. Therefore, the addition of hydrogen would not benefit neither maintaining the catalyst stability nor improving the crystallinity of the CNT products. The kinetic model of CNTs formation, derived from the two types of active site of dissociative adsorption of methane, corresponded well to the experimental results. The rate of CNTs formation greatly increases with the partial pressure of methane but decreases when saturation is exceeded. The activation energy was found to be 13.22 kJ mol-1, showing the rate controlling step to be in the process of mass transfer.

Synthesis of boron-doped carbon nanotubes by thermocatalytic decomposition of ethanol using a floating catalyst chemical vapor deposition method: kinetic study

The effect of different reaction parameters helped in understanding the structure–property relationship in B-doped CNTs. A plausible reaction kinetic model and a reaction mechanism were proposed for the FCCVD synthesis of BCNTs.

Catalytic Methane Decomposition to Carbon Nanostructures and COx-Free Hydrogen: A Mini-Review

Catalytic methane decomposition (CMD) is a highly promising approach for the rational production of relatively CO_x-free hydrogen and carbon nanostructures, which are both important in multidisciplinary catalytic applications, electronics, fuel cells, etc. Research on CMD has been expanding in recent years with more than 2000 studies in the last five years alone. It is therefore a daunting task to provide a timely update on recent advances in the CMD process, related catalysis, kinetics, and reaction products. This mini-review emphasizes recent studies on the CMD process investigating self-standing/supported metal-based catalysts (e.g., Fe, Ni, Co, and Cu), metal oxide supports (e.g., SiO₂, Al₂O₃, and TiO₂), and carbon-based catalysts (e.g., carbon blacks, carbon nanotubes, and activated carbons) alongside their parameters supported with various examples, schematics, and comparison tables. In addition, the review examines the effect of a catalyst’s shape and composition on CMD activity, stability, and products. It also attempts to bridge the gap between research and practical utilization of the CMD process and its future prospects.

Enhanced adsorption of As(V) and Mn(VII) from industrial wastewater using multi-walled carbon nanotubes and carboxylated multi-walled carbon nanotubes

The presence of As(V) and Mn(VII) in water beyond the permissible concentration allowed by World Health Organization (WHO) standard affects human beings, animals and the environment adversely. Hence, there is need for an efficient material to remove these potentially toxic elements from wastewater prior to discharge into water bodies. This research focused on the application of response surface method (RSM) assisted optimization of Fe-Ni/Activated carbon (AC) catalyst for the synthesis of MWCNTs. Also, the MWCNTs was carboxylated and the adsorption behaviors of both nano-adsorbents in the removal of As(V) and Mn(VII) from industrial wastewater was investigated through experimental and computational techniques. The prepared Fe-Ni/AC, MWCNTs and MWCNTs-OCH₂CO₂H were characterized using BET, TGA, FTIR, HRSEM, HRTEM, XRD and XPS. The result showed the BET surface area of Fe-Ni/AC, MWCNTs and MWCNTs-OCH₂CO₂H were obtained as 1100, 1250 and 1172 m²/g, respectively. Due to the enhanced impact of carboxylation, the adsorption capacity of As(V) and Mn(VII) removal increased from 200 to 192 mg/g for MWCNTs to 250 and 298 mg/g for MWCNTs-OCH₂CO₂H. The isotherm and kinetic models were best fitted by Langmuir and pseudo-second order kinetics, while the thermodynamic investigation found that the adsorption process was endothermic, spontaneous and chemisorptions controlled. The regeneration potential of MWCNTs and MWCNTs-OCH₂CO₂H after six repeated applications revealed good stability of adsorption efficiency. The study demonstrated optimization importance of Fe-Ni/AC catalyst design for MWCNTs adsorbents and the potentials of utilizing both MWCNTs and MWCNTs-OCH₂CO₂H in the removal of selected heavy metals from water and soil.

Double-walled hierarchical porous silica nanotubes loaded Au nanoparticles in the interlayer as a high-performance catalyst

Double-walled hierarchical porous silica nanotubes (NTs) loaded Au nanoparticles (Au NPs) in the interlayer (SiO₂@Au@SiO₂ NTs) are synthesized by using tetraethoxysilane as silica source and hollow polydivinylbenzene (PDVB) nanowires as the sacrificial templates. The mesopores on the walls and the hollow structure of NTs (macropores) construct the hierarchical porous structure. The SiO₂@Au@SiO₂ NTs possess a high surface area of 405 m² g^-1 and an average pores size of 4.7 nm. The double-walled structure protects the Au NPs from environmental attacks, which shows an excellent catalytic activity even after reusing 10 times. Meanwhile, the hierarchical porous structure shows excellent catalytic ability and allows the catalytic reaction process to be completed within 5 min. This result indicates that double-walled silica NTs have vast potential in catalysis application due to the special structure.